The pilings are on land.
It’s a cantilever bridge. Set a concrete block on one side of a creek, another across the way, then balance a 2x10 on each block, so that they meet in the middle. If one block fails, then whole structure becomes unstable.
This bridge is comprised of two such structures side by side, at the upstream and downstream edges of the deck. The two structures are joined together by diagonal bracing between them, designed to keep a cross section of the structure square and upright.
It appears to me that the steel structure above one pier failed laterally, as if the diagonal braces between the kingposts atop both same side concrete piers failed under comprension or tension allowing the bridge deck to sway in the downstream direction before toppling over on its side.
On the far side, the steel trusses suffered shearing failure directly above the piers, dropping the main span into the river nearly intact. Then the approach span on that side lost its counterweight, began to buckle, and collapsed back towards the shore.
Having fished under where that bridge is in my much younger years I’ll tell you theres a lot of current right there even with the record low levels we have this year. I do a little fishing on the Miss and live on it, the river does whatever it wants, and don’t always tell you about it.